Polymeric staple fiber blend containing weakened polyamide fibers



United States Patent 3,293,110 POLYMERIC STAPLE FIBER BLEND CONTAINING WEAKENED POLYAMIDE FIBERS William H. Stine, Jr., and Ira G. Epstein, Wilmington,

Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed June-26, 1962, Ser. No. 205,193

Claims. (Cl. 161-169) This invention relates generally to the production of staple fibers and, more particularly, to blends'of such fibers.

Fibers prepared from synthetic linear polymers have proved superior to natural fibers in many respects, some being particularly noteworthy for their increased strength and durability. However, when staple lengths of these fibers are employed in many end uses, such as in loosely woven fabrics, certain types of carpets and the like, the finished article often becomes unsatisfactory in appearance after short usage due to excessive pilling and fuzzing. Pilling refers to the formation of little balls of fibers on the surface of the finished article due to entanglement of loose fibers. Less well defined entanglements are called fuzz.

There have been many attempts in the past to eliminate pilling and fuzzing by various fiber and fabric treatments, all of which have generally met with limited success. Recently, however, a polyamide fiber has been developed which has Weak spots spaced through the length thereof. In textile articles prepared from staple lengths, pilling and fuzzing are reduced to acceptable levels due to breakage of the anchoring fibers at weak spots. Furthermore, since connecting portions of the staple lengths are relatively unaffected by the procedures followed in introducing the weak spots, their average abrasion resistance is high and the durability of articles prepared therefrom is much higher than can be obtained with natural fibers. For instance, carpets prepared from crimped polyamide staple fibers of this type not only exhibit'satisfactory pilling and fuzzing performance but also have a durability three or four times that of wool. These pill-resistant nylon fibers have been described by Matray and Stine in copending application Serial No. 94,447, filed March 9, 1961, now US. Patent No. 3,050,822. w

The most important object of the present invention is to provide a synthetic staple fiber blend especially adapted for use in the fabrication of durable, pill-resistant textile articles. 7 Y

A more particular objective is to provide a staple fiber blend with which improved levels of durability, hand and aesthetics can be achieved in textile articles such as carpets.

Another important object is to facilitate the production of textile articles which, in addition, are more resistant to both soiling and the development of static electricity.

These and other objectives are accomplished with a blend of crimped, low-denier, low-toughness, long, polyamide, staple fibers and crimped, high-denier, high-toughness, short, synthetic, polymeric, staple fibers, all of which initially contain a minor weight percentage of a poly(alkyl ether). In order to achieve optimum aesthetics, the denier and crimp in each component of the blend should be related inversely, i.e., for an increase in denier, the crimp frequency should be decreased. The long fibers of the blend have a staple length of atleast three inches, a crimp frequency of about 8-22 crimps/inch, a "denier of about 815 and a loop toughness of about 2-27 whereas the short fibers have a staple length of about /22 inches, a crimp frequency of about 6-12 crimps/inch, a denier of about 22-35 and a loop toughness of at least 50. There are from 25-90% by weight of low toughness fibers in the blend.

3 ,Z93',l l0 Patented Dec. 20, 1966 As disclosed in detail by Matray and Stine, the low toughness fibers have frequentspaced weak spotsin' each staple length andare characterized as to weak spot frequency and severity by a significant decrease inbreak tenacity with increases in length from a zero :test length as well as by the occurrence of at least one weak spot/ inch. Weak spot frequency and severity are further characterized by a value of less than about 0.80 for the ratio'of T T where T and T are the break-tenacities of one inch and zero length samples, respectively. A loop toughness value of from about 227 is also indicative of weak spot severity. When the blend is to beused in the preparation of carpets, loop toughness is preferably in the range of 415.

Finished articles prepared from the fiber blends of this invention maybe made resistant to the build-up of static charges by incorporating a minor weight percentage of a durable antistatic agent in the higher toughness fibers. This is accomplished-by adding a suitable agent, e.g., one of the poly(alkyl ethers), to the molten polymer prior to its extrusion. The antistatic agent cannot be permanently incorporated in-the low toughness fibers, since the treatment required to lower the toughness of the fibers renders the antistatic agent nonpermanent, i.e., it is readily Washed out. In the practice of the present invention, at least about 2% by weight is required in order to achieve a significant reduction in the tendency to develop static charges and the concentration in the high toughness fibers is preferably in the range of 310%. Where the amount of high toughness fibers in the blend is small, even larger concentrations may be needed. The preferred antistatic agent is polyethylene ether glycol having a molecular weight of 1000-50,000.

Resistance to soiling is imparted to the fibers by the presence of small internal voids which are formed when a portion of the anti-static agent is removed from the high toughness fibers during fabric finishing. The antisoiling characteristics of the blend may be further improved'by producing similar-voids'in the low toughness fibers by incorporating therein an initial small-amount 0f the antistatic agent or some other suitable material which leaves small internal voids when removed from the fiber by hot aqueous treatment such as commonly used inthe finishing of textile articles. These voids increase the reflection and decrease the transmission of light through the fibers.

The long and short fibers may be blended together by hand'or by the use of'any suitable blending equipment such as, for instance, a Proctor and Schwartz woolen system blender. Effective and complete blending at this stage is in general not critical, since further blending to achieve the necessary intimate association'of fibers is accomplished when they are subsequently processed. into spun yarn.

In the following examples, loop toughness, T and T values are determined as described by Matrayand-Stine.

Example I Polyhexamethylene adipamide having a relative viscosity of 45 is'prepared and melt extruded to produce a yarn consisting of 34 filaments of 46 denier each. The yarn is cold drawn to a drawratio of 4.05 and a number of yarn strands plied together to give a 'tow of 4,000 filaments of 12 denier each. i This plied yarn is crimped by passing it through a st'ufier box crimper where it is sub jected'to sufficient pressure to provide anaverage of '15 crimps per inch in the filaments, cut into 4 /2 inch staple fiber, placed in glass fiber bags and soaked in a 9% aqueous solution of hydrogeneroxide for 30 minutes at room temperature after which it is centrifuged touremove excesssolution. The centrifuged tow, containing 12% of peroxide solution based on the dry weight of the fiber, is placed in a wire basket and moved to an autoclave where it is steamed for -1 hour at 28 p.s.ig. pressure. After drying, the severity and frequency of the induced weak spots are determined by measuring the breaking tenacity of twenty-five random zero length and 1 inch samples. Breaking tenacity T for the 1 inch samples is found to be 1.23 g.p.d. and that of the zero length sample 1.85 g.p.d., giving a value of 0.67 for the ratio T /T The loop toughness of filaments removed from the tow is measured and found to be 6.2. The 4 /2 inch staple 'fiber is then blended with an equal Weight of 1 /2 inch staple fiber cut from a 27 d.p.f., 8 crimps/inch polyamide tow prepared as described above except for elimination of the peroxide treatment. The blending is carried out using a Proctor and Schwartz woolen system blender. The resulting blend is processed into 2/55s yarn, Philadelphia system, using the conventional wool process, given a single twist of 4.5Z and a ply twist of 3.08 and woven into a 30 oz. per sq. yard, 198 pitch, plain velvet weave, loop pile carpet having 8 rows/inch in the warp direction, the wire height of the loom being 0.375 inch. For comparison, carpet is also prepared from 100% peroxide treated fibers. Wool carpets of similar construction are also obtained for comparison.

The different carpets, in 7 x 26 inches samples, are tested under secretaries desks. Samples are rotated within a desk once each day and between desks every five days. All samples are vacuum cleaned twice per week. Evaluations of the test carpets are made every ten days by a panel of three experts in the carpet field. The test samples are given a rating in the range of 1 to 5, 1 indicating very severe pilling and fuzzing and indicating the condition of the carpet as woven. The results of these tests are given in Table I below.

TABLE I Pilljng and Fuzzing Rating Length of test, days 10 20 30 40 50 60 70 Example 11 A staple fiber blend is prepared and processed into carpet as described in Example I except that the blend consists of 50% peroxide treated 3 inch staple fiber having'a loop toughness of '7 and 50% 1 inch untreated fiber having a loop toughness of 200. When the durability of this carpet is determined and compared with a carpet prepared from 100% of the peroxide treated fiber, the durability of the blended fiber carpet is found to be approximately twice that of the other. The results obtained when the carpet is tested for pilling and fuzzing as described in Example I are recorded in Table II. The eiiects of a reduction in staple lengths are apparent from a comparison with the results obtained in Example I.

Example III Crimped tow is prepared as describedin Example I p and treated with 13% aqueous hydrogen peroxide solution to produce a fiber having a loop toughnessof 3.5. The tow is cut to 3 inch staple and a blend is prepared containing of this fiber and 10% of 3 inch staple fiber prepared in the same manner except for the peroxide treatment. The blended fiber is processed into a carpet and evaluated for pilling and fuzzing as described in Example I. In comparison with carpet prepared from of the peroxide treated fiber, the blended fiber carpet exhibits substantially worse pilling and fuzzing and it is observed that after 30 days of testing the blended fiber carpet had formed pills which were anchored by the 3- inch, high-toughness nylon fibers even though they were present at a concentration of only 10% by weight.

Example IV A 48% aqueous solution of hexamethylene diammonium adipate (66 nylon) and 0.3 percent (based on the salt) of a 25% aqueous acetic acid solution (viscosity stabilizer) are charged to an evaporator and concentrated to 60% at atmospheric pressure. The 60% salt solution is transferred to an autoclave equipped with a stirrer and is heated in the closed vessel until the steam pressure reaches 250 p.s.i. and a temperature of 210 C. over a period of about 20 minutes. The autoclave stirrer is then started. Heating is continued to a temperature of 235 C. at which time a 25% aqueous solution of polyethylene ether glycol of 6000 molecular weight is pumped in. Sufficient of the polyether is added to correspond to 1.0% of the weight of the polymer. Heating is continued, the temperature increasing, while maintaining a pressure of 250 p.s.i. by bleeding off steam. When the temperature reaches 240 C., steam is bled oif more rapidly, reducing the pressure continuously over about 90 minutes to atmospheric pressure. Heating at atmospheric pressure is continued at about 275 C. to complete the polymerization. The autoclave is discharged by extruding the polymer as a ribbon at 100 lbs. pressure of inert gas. The ribbon is quenched on a water cooled casting wheel and cut toflake having a relative viscosity of 40. This batch of polymer is designated polymer A. In similar fashion, polymer B containing 2% by weight of the polyether, polymer C containing 5% by weight of the polyether, polymer D containing 7.5% of the polyether and polymer E containing 20% of the polyether are prepared.

Polymer A is melt extruded in the conventional manner to produce a yarn of 23 filaments. The yarn is cold drawn at a ratio of 4.05, the drawn filaments having a denier of 12. The drawn yarn is plied to give a tow of 4,000 filaments, crimped as described in Example I to give a crimp frequency of 15 crimps/inch and cut into 6-inch staple fiber which is treated with aqueous peroxide solution of 10% concentration as described in Example I to produce a fiber having a loop toughness of 6.

Polymers B, C, D and E are melt extruded, cold drawn and crimped as described above to give crimped tows of 27 denier per filament and 8 crim-ps/inch. These tows are cut into 1 /2 inch staple fibers. Fibers B, C, D and E all have loop toughness values of about 100.

Each of fiber batches B, C, D and E are blended with an equal weight of fiber A to produce fiber blends AB, AC, AD and AE, all of which are scoured by boiling for 1 hour in an aqueous solution containing 0.1% of trisodiumphosphate and 0.125% of Alkanol HCS, a liquid nonionic detergent. The fiber is then rinsed to remove the detergent and mock dyed by boiling for 1 hour in an aqueous solution containing 0.04% of capracyl levelin-g salt and 0.02% of ammonium hydroxide followed by addition of 0.1% ammonium sulphate and further boiling for 1 hour after which the fiber is rinsed thoroughly. The fiber is then dried to a moisture content of about 4% After scouring and mock dyeing, analysisof the long fibers (fiber A) shows that all of the po/lyether has been removed, leaving tiny internal voids which increase the opacity of the fiber and increase its ability to reflect light.

Fiber Aand fiber blends AB, AC. AD and AE are processed into carpets as described in Example I. The performance of the carpets with respect to development of a static charge is measured by placing the carpets in a conditioned room at 20% relative humidity and 70 F. and measuring the voltage generated by an individual Walking onth'e'test carpet using an electrostatic Volt are shown in Table VI below. For comparison, results are also shown on 100% peroxide treated fiber carpet and on conventional nylon carpet. The degree of soiling was determined by a panel of judges expert in the carpet field.

meter. Results of these tests'ar'e shown in Table III 5 The carpets were rated'fhom 1 to 5, a rating of 5 being below. For comparison, results are also shownon clean given to the unsoiled carpet as laid down and a rating of and soiled wool. 1 for severe soiling.

TABLE III TABLE VI Fiber A AB AC AD An c i iee i sane 10 Tratfic cycles, thousands 0 4 s 12 16 l l l Fiber blend AD 5.0 3.4 2.7 2.6 2.6 Kilovolts 11 9.5 9 6.4 6.2 9.5 5 100% H202 treated 5.0 2.8 2.6 1.7 1.3 Conventional nylon 5. 0 2. 3 2. 0 1. 3 1. 0 The fuzzing and pilling performance of the car-pet pre- 15 pared from fiber blend AD is determined as described in Example VII Example I. Results of this test are shown in Table IV, below. For comparison, carpets of wool and of 'convenp 16 g f g i a gg gggg ig 6:2 2 tiollal mped nylon staple are tested simultaneously With 2 fif i g i g g is 18 and the results being recorded in Table IV. 0 O mp e P the crimp frequency 1s 12 crimps per inch. A high tough- TABLE Iv ness staple fiber containing 5% of the polyethylene ether glycol is prepared as described for fiber C of Example l e and Pmmg IV except hat the filament denier is 18 and the crimp fre- L quency is 12 crimps per inch, i.e., the same as for the ,ength of test days 10 20 40 low toughness fibers. Equal parts of the high and low Fiber blend AD n 3.4 2.7 2-5 2.0 toughness fibers are blended and processed into a oz./ WM"; 23 L7 L7 1 9 sq. yd. carpet as described in Example I. When this car- Nylon staple. 1.5 0.5 0.7 O 3 pet is tested for pilling and fuzzing as described in EX- 30 ample I, in comparison with a carpet of the same con- When the durability of the carpet from fiber blend AD s ru i n pr par from blend AC of Example IV, he is determined as described in gxainple I and compared CaTPet from fiber blend AC proves to 136 considerably with that of 100% peroxide treated fiber carpet and wool p ri r n p rf m n e. Th rp fr m b n AC i car-pet, it is found to have a durability about twice that also judged to be superior in hand, aesthetics and apof th 100% ide treated fiber carpet and about eight pearance. This illustrates the advantages in pilling and times th mf -1 Carpet fuzzing and in aesthetics to be desired from the combination of high denier, short fibers and lower denier, long E xample V fibers in the blend.

Carpets are prepared as described in Example I from Example VIII 1 :3 t of EXPmPIe IV except that the pile yam 40 Staple fibers F and G are prepared as described for e-up is varied to give carpets of 24, 26, 28 and 30 oz. fib

. Y er A of Example IV except that fiber F has a filament per sq. yd. Carpets are prepared n a similar fashion,

denier of 15 and a crimp frequency of 12 crimps/inch using wool and conventional crimped nylon staple. r

e a while fiber G has a filament denier of 8 and a crimp fre- Aesthetics of hand and appearance for each carpet are f 22 h d G 11 then determinedby presentin the sam le t f d quency o crimps 1 ers F an ale eac I g psoour uges I v blended with an equal weight of fiber D of Example IV who are expert n th s field. The results are determ ned to form fiber blends PD and GD These blends re from a series of matched comparisons wherein each item then rocessed into 30 OZ /S d et d is compared with every other item being tested. In this E p y arp as escn m v 1 r I c xample I. When the carpets are tested as previously test, each item 18 paired successively w th all the other described the min and fuzz-in erfo a f d items and each pair pres nt d to 1 lll an opinion to be satisfacto r is about e uil io th a i 01?; 1S d ih as to which of the two items is superior in hand and apq me A e similar carpets from fiber blend AD of Examples IV, V pearance. The results shown in Table V below indicate and V I. From an aesthetic standpoint, the carpet from the percentage of the time a particular item was selected fib b1 d FD d d b 1 as the superior of twobeing compared Thus the number er en 1S ge to e equlva em to the carpet v v from fiber blend AD but the car et from fiber blend GD 37 for the blend AD 24 oz carpet indicates that this item p Y A a lightly poorer than that from AD althou h still conwas selected as superior 37% of the time when com- I? S g siderably superior to that obtained with conventional pared with all the other items being tested. The convenr nylon or with carpets from 100% of fiber A of Example mortal nylon i fiber usgd in thevca'rpet test-ed for IV The carpet from fiber blend FD exhibits a slight loss g i g g g arm-1P f-rregig-ngy of 12 cnmps per mch and in covering power as compared to that from fiber AD al- 0 though the covering power is still quite satisfactory. The TAB E V carpet from fiber blend GD exhibits an improved covering power as compared to the carpet from fiber blend AD. Favorable 5919011011, Percent Resistance to soiling and static and durability are about the same for ca ets fro bl d Yd a a m GD and AD 1 er en 5 Wo 32 46' 3 i IX 16 22 24 31 Staple fibers H and K are prepared as described for fiber D of Example IV except that fiber H has a filament Example ifilii fiiifh fia s1353 363 323 f4? F ier 0 an a crim A 30 oz. carpet prepared as described in Example I frequency of 6 crimps/inch. Fibers H and K are 6365 from fiber blend AD of Examples IV, .V is testedfor soil blended with an equal weight of fiber A of Example IV resistance by placing it .in a hallway where it was subto forrn fiber blends AH and AK. These blends are then jected to severe traffic, the number of traffic cycles being rocessed into 30 oz./sq. yd. carpet as described in Exdetermined by an electronic counter. Results of this test ample I. When the carpets are tested as previously dew a scribed in comparison with a similar carpet from fiber blend AD of Examples IV, V and VI, the carpets from blends AH and AK are found to have a pilling and fuzzing performance substantially equivalent to the carpet from fiber AD. The carpet from fiber blend AH exhibits slightly poorer aesthetics but slightly better covering power than the carpet from lend AD. The carpet from fiber blend AK exhibits slightly better aesthetics but slightly poorer covering power than the carpet from fiber blend AD. The durability and resistance to soiling and static of the carpets from fiber blends AH and AK are substantially equivalent to those of the carpet from fiber blend AD.

Example X A 30 oz./sq. yd. carpet is prepared as described in Example I from a blend containing 90% of fiber A of Example IV and of fiber E of Example IV. When tested in comparison with a carpet prepared from 100% of fiber A, this carpet shows substantial improvement in durability and equivalent fuzzing and pilling performance. The carpet from the blend is also improved with respect to soiling and resistance to buildup of static charge.

Example XI A 30 oz./ sq. yd. carpet is prepared as described in Example I from a blend containing 25% of fiber A of Example IV and 75% of fiber D of Example IV. When compared with a carpet prepared from 100% fiber A, this carpet is found to have much greater durability, resistance to soiling and resistance to buildup of static charge but tends to develop fuzz on the surface and is therefore somewhat inferior in appearance to carpet from 100% fiber A although much superior to a carpet from 100% conventional nylon staple fiber.

As illustrated in the foregoing examples, the fiber blends disclosed herein may be utilized to produce carpets of improved durability, aesthetics, soiling characteristics and resistance to static electricity, while retaining a desirably high resistance to pilling and fuzzing.

The preferred fibers for use in preparing the blends of this invention are the nylon fibers, these being produced from synthetic linear polyamides in accordance with procedures well known in the art. Nylon fibers are particularly suitable for use in the instant blends since the low-toughness, high-toughness combination provides an excellent balance between pilling-fuzzing performance and durability. Especially suitable for use are those prepared fnom polyhexamethylene adipamide, polyhexamethylene sebacamide, polyhexamethylene isophthalamide or polycaproamide. Among the other suitable polyamides are those disclosed in US. Patents Nos. 2,071,253, 2,130,- 523 and 2,130,948. Interpolyamides prepared from mixtures of diamines, dibasic acids and amino acids can also be used for the practice of this invention. Likewise, melt blends of two or more polyamides can be used as a source of suitable fibers. Synthetic fibers other than polyamides may be used in the high toughness component of the blend. Among the fibers which are suitable for this purpose are the polyesters, such as polyethylene tel-ephthalate, the polyvinyl fibers such as polyacrylonitrile fiber and the polyolefin fibers such as polyethylene or polypropylene fibers.

The percentage of high toughness fibers in the blend may be varied somewhat depending on the fiber selected and its toughness. With lower loop toughness values, larger amounts may be used Without adverse effects on milling and fuzzing performance. In general, however, the amount should not exceed 75% by weight of the blend and preferably no more than about 60% is used since processa-bil-ity in the woolen system is adversely aftfected by excessive amounts of short fibers. The smallest amount which will give beneficial effects depends on the toughness level. However, even with fibers of very :high toughness, at least about 10% should be present to 8 v yield appreciable improvements. -In this respect, it is difiicult to obtain the desired anti-static effect with small amounts of the high toughness fiber since this component of the blend carries all of the anti-static agent. When all of these factors are considered in connection with the higher production costs for the low toughness fibers, amounts in the range of 4060% of the high toughness fibers are preferred.

'In the practice of this invention, a substantial improvement in pilling and fuzzing is obtained in carpets the short fibers in the blend are relatively high denier, i.e., in the range of 20 to 40 denier/ filament. It is preferable when using fibers .in this range that the longer fibers be of substantially lower denier in order to provide the necessary cover in the carpet or other textile article. Prefer-- ably, the longer fibers are in the range of 8 to 15 'dener/ filament. Also, it is desirable that the crimp frequency of the short higher denier fibers be in the range of 6 to 12 chimps/inch and that the crimp frequency of the longer fibers be in the range of 8 to 22 crimps/inch in order to provide the maximum improvement in aesthetics (Examples VIII and IX). A higher crimp (frequency in the short fibers leads to harshness or scratchiness while lower crimp causes low cohesion and poor woolen system processability. Crimp frequency in the longer fibers is likewise limited byprocessa'bility and aesthetics.

Poly(alkyl others) suitable for use as an antistatic agent include the condensation prod-nets of either ethylene oxide, propylene oxide or ethylene oxide-propylene oxide. These condensation products contain from two to three carbon atoms in the alkyl group with two of the carbon atoms being intralinea-r carbon atoms connecting intralinear ether-oxygen atoms. Preferably, the poly(-alkyl ether) is an ethylene oxide polymer which may be terminated or capped by hydroxyl'igr-oups or by one or more ether end groups of the formula OR, where R is an alkyl, aryl, or aralkyl group, such as methyl, ethyl, i-ootyl, decyl. lauryl, tridecyl, nonylphenyl, dodeeylphenyl, phenyl, napht-hyl or the like. Residues of coupling compounds or chain-initiating agents, such as bisphenol, may be present. The po1y(a1'-kyl ether) may, as just mentioned, be a propylene oxide polymer or an ethylene oxide-propylene oxide copolymer. Indeed, when the specified number of ethylene oxide uni-ts are present, copolymer constituents in addition to those mentioned may be included in the polymer chain. Other elements or radicals may be introduced into the R groups provided they are not reactive with the hydrophobic polymer, e.:g., halogen, especially fluorine, a phosphite or phosphate to decrease flammability, and hyphosphite or phosp'hinate to improve light durability. The need for avoiding groups which are reactive with the hydrophobic polymer will be readily apparent since durability, molecular weight, and other physical properties of the hydrophobic polymer are adversely affected by copolymeriza-tion with poly(alkyl ethers).

Poly(alkyl ethers) have molecular weights in the range of 600 to 3,000,000 may be used but the preferred range is l000-50,000. Suitable tpoly(alikyl ethers) include polyethylene ether glycols having molecular Weights of 20,000, 200,000, 500,000 and 3,000,000; polypropylene ether glycol having a molecular weight of 2000 and polyethylene ether .glycols capped with nonyl phenyl groups and having molecular weights of 600, 1 600 and 4600.

While the preferred taxtile product of this invention is carpets, particularly loop pile carpets, other knitted and woven structures such as blankets, sweaters, fiannels, hoisery and suitin-gs may be made to advantage from the fiber blends disclosed herein. The fibers in the two components of which a given blend is comprised may, of course, be varied within the limitations specified previously with respect to denier, length, toughness and crimp frequency. Such variations are, in some cases, helpful in achieving the optimum level of aesthetics or durability and in obtaining the lowest level of pilling or fuzzing. Minor components of other fibers may, if properly selected, be incorporated in the blend without deleterious effects and, in some instances, benefits may be derived from such additions. For instance, a small amount of long, low denier, hightoughness fiber may be added to improve processability of the blend without seriously impairing its desirable characteristics. Similarly, minor amounts of wool or of another synthetic fiber such as polyethylene may be added if desired. It is apparent that other variations and modifications may be made in the disclosed fiber blend without departing from the spirit of the present invention which is accordingly intended to be limited only by the scope of the appended claims.

We claim:

1. A blend of synthetic staple fibers, said blend being comprised of first and second components, the first component being crimped polyamide staple having frequent spaced weak spots in the length thereof, said staple being characterized as to weak spot frequency and severity by a significant decrease in break tenacity with increases in length, a crimp frequency of from 8-22 crimps/inch, a denier of from 8-15, a loop toughness of 2-27 and a staple length of at least three inches, the second component being erimped polymeric staple characterized by a crimp frequency of 6-12 crimps/inch, a denier of from 20-40, a loop toughness of at least 50 and a staple length of no more than about two inches, there being at least 25% by Weight of said first component in the blend.

2. A blend comprised of crimped, low-denier, lowtoughness, long, polyamide, staple fibers and crimped, high-denier, high-toughness, short, synthetic, polymeric, staple fibers, there being from 25-90% by weight of the low-toughness fibers in the blend.

3. The blend of claim 2 wherein the long fiber have a staple length of at least three inches and the short fibers have a staple length of at least one inch.

4. The blend of claim 3 wherein all of said staple fibers are further characterized by the presence of small internal voids.

5. A blend of crimped, low-denier, low-toughness, long, polyamide, staple fibers and crimped, high-denier, high-toughness, short, synthetic, polymeric, staple fibers, said short fibers containing a minor weight percentage of a poly(alkyl ether), there being at least 25 by weight of long fibers in the blend.

'6. The blend of claim 5 wherein said short fibers contain about 2-20% by weight of said poly(alkyl ether).

7. The blend of claim 6 wherein said long fibers have a crimp frequency of about 8-22 crimps/inch, a denier of about 8-15 and a loop toughness of about 2-27.

8. The blend of claim 7 wherein said short fibers have a crimp frequency of about 6-12 crimps/inch, a denier of about 22-35 and a loop toughness of at least 50.

9. A blend of crimped, low-denier, low-toughness, long, polyamide, staple fibers and crimped, high-denier, hightoughness, short, polyamide, staple fibers, said low-toughness fibers having frequent, spaced, weak spots in each staple length and being characterized as to weak spot frequency and severity by a significant decrease in break tenacity as the staple length is increased from a zero test length and by the occurrence of at least one weak spot/inch, there being at least 25% by weight of lowtoughness fibers in the blend.

10. A blend of crimped, low-denier, low-toughness, polyamide, staple fiber and crimped, high-denier, hightoughness, short, synthetic, polymeric, staple fibers, said low-toughness fibers having frequent, spaced, weak spots in each staple length and being characterized as to Weak spot frequency and severity by a value of les than about 0. for the ratio T T 0 Where T is the break tenacity of a one inch sample and T is the break tenacity of a zero length sample, said low-toughness fibers being further characterized as to weak spot severity by a loop toughness of from 2-27, there being at least 25 by weight of low-toughness fiber in the blend.

References Cited by the Examiner UNITED STATES PATENTS 2,816,349 12/1957 Pamm et al 28-82 2,909,404 10/ 1959 Dithrnar et al 8-1 11 3,008,215 11/1961 Pitts 57-157 3,046,724 7/1962 Ward 57-140 3,050,822 8/1962 Matray et a1 2882 FOREIGN PATENTS 513,033 1939 Great Britain. 870,017 6/ 1961 Great Britain.

ALEXANDER WYMAN, Primary Examiner.

RUSSELL C. MADER, L. K. RIMRODT,

Assistant Examiners. 

1. A BLEND OF SYNTHETIC STAPLE FIBERS, SAID BLEND BEING COMPRISED OF FIRST AND SECOND COMPONENTS, THE FIRST COMPONENT BEING CRIMPED POLYAMIDE STAPLE HAVING FREQUENT SPACED WEAK SPOTS IN THE LENGTH THEREOF, SAID STAPLE BEING CHARACTERIZED AS TO WEAK SPOT FREQUENTLY AND SEVERITY BY A SIGNIFICANT DECREASE IN BREAK TENACITY WITH INCREASES IN LENGTH, A CRIMP FREQUENCY OF FROM 8-22 CRIMPS/INCH, A DENIER OF FROM 8-15, A LOOP TOUGHNESS OF 2-27 AND A STAPLE LENGTH OF AT LEAST THREE INCHES, THE SECOND COMPONENT BEING CRIMPED POLYMERIC STAPLE CHARACTERIZED BY A CRIMP FREQUENCY OF 6-12 CRIMPS/INCH, A DENIER OF FROM 20-40, A LOOP TOUGHNESS OF AT LEAST 50 AND A STAPLE LENGTH OF NO MORE THAN ABOUT TWO INCHES, THERE BEING AT LEAST 25% BY WEIGHT OF SAID FIRST COMPONENT IN THE BLEND. 